Actuator with self-protecting limiting mechanism



Nov. 30, 1965 v. A. HOOVER 3,221,118

ACTUATORWITH SELF-PROTECTING LIMITING MECHANISM Original Fi1ed SeptQ5,1957 INVENTOR VWNO A 1 /00 nae United States Patent 3,221,118 ACTUATORWITH SELF-PROTECTING LIMITING MECHANISM Vaino A. Hoover, 1433 SanVicente Blvd, Santa Monica, Calif.

Original application Sept. 5, 1957, Ser. No. 682,121, now Patent No.3,087,105, dated Apr. 23, 1963. Divided and this application June 13,1962, Ser. No. 202,170

5 Claims. (Cl. 20047) The present application is a division of my priorcopending application entitled Electromechanical Actuator With LimitingMechanism, Serial No. 682,121, filed September 5, 1957, now Patent No.3,087,105.

This invention relates generally to electromechanical actuators, andmore particularlyto an actuator embodying an improved mechanism forlimiting the movement of its output member.

Electromechanical actuators have been found to be very effective meansfor actuating movable parts. One of the principal applications for theseactuators is in modern aircraft, where they are used for such purposesas the actuation of trim tabs and the like. Such actuators also serveeffectively in many other applications, including industrial automation.

In most applications of actuators of the subject type, it is anoperational requirement that movement of the output member be accuratelycontrolled within predetermined limits. To achieve this, the actuator isequipped with a limiting mechanism which serves to terminate operationof the actuator in a given direction, when the driven device has reacheda corresponding limit position. It will be readily appreciated that,particularly in aircraft applications where a malfunction is potentiallydisastrous, the operation of the actuator must be as foolproof aspossible. Moreover, the operation of the limiting mechanism isespecially crucial. A malfunction of the limiting mechanism is likely toresult in damage to the mechanism itself, as well as to other parts ofthe actuator and driven device.

It is, therefore, extremely important in such actuators, not only thatthe limiting mechanism be as troublefree as possible, but also thatadditional protective means be provided which will prevent damage in theevent a malfunction should occur. It is in this latter regard that prioractuators have been particularly lacking.

Another requisite feature of actuators in aircraft and many otherapplications is that they be constructed and arranged so that the limitpositions of the output member can be adjustably established. This isnecessary for the reason that the part to be actuated normally hasmanufacturing tolerances. Moreover, additional tolerances frequentlydevelop during assembly. To compensate for such tolerances and insurethat the limit positions of the actuator and its associated drivendevice coincide, it is necessary to provide for final adjustment afterassembly.

Further operational requirements of such actuators in aircraftapplications are that, in addition to the above capabilities, the devicebe sufficiently sturdy to withstand sustained vibration and rapidlyfluctuating atmospheric conditions, and be relatively light in weight.

It is, therefore, a major object of this invention to provide anelectromechanical actuator embodying a limiting mechanism, whichsatisfies all of the above requirements.

Another object is to provide an electromechanical actuator with alimiting mechanism for accurately controlling movement of its outputmember within predetermined limits, the mechanism incorporating meansfor protecting it from damage in the event of a malfunction.

3,22 l ,1 l8 Patented Nov. 30, l 965 It is a further object of thisinvention to provide an actuator of the type described in which thelimiting mechanism can be either manually adjusted to accuratelyestablish the limit positions desired or automatically adjusted so thatthose positions substantially coincide with the mechanical limits of thedriven device.

Another object of this invention is to provide a compact, lightweightactuator of the type described which comprises a minimum number ofcomponent parts, and which is relatively simple in construction andinexpensive to manufacture.

These and other objects, features, and advantages of the invention willbe better understood by referring to the following detailed descriptiontaken in conjunction with the accompanying drawing of an illustrativeembodiment, in which:

FIGURE 1 is a side view, partly in elevation and partly in section, ofthe actuator of the invention, showing the limiting mechanism in one ofits limit positions;

FIGURE 2 is a partial sectional view taken along the line 22 of FIGURE1; and

FIGURE 3 is an enlarged sectional view of the area encircled by the line3 of FIGURE 1, showing the limiting mechanism in its limit positionopposite that occupied in FIGURE 1.

Referring to the drawings, and in particular to FIGURE 1 thereof,numeral 10 designates the actuator of the invention. The actuator 10includes generally a reversible electric drive motor 12, a magneticclutch and brake unit 14, reduction gearing 16, and a limiting mechanism18. As illustrated, the motor is coupled through the clutch and brakeunit 14 and the reduction gearing 16 to a rotatable output shaft 20. Themotor 12 is adapted to be selectively energized so as to drive the shaft20 clockwise or counterclockwise, as viewed from the right hand end ofFIGURE 1.

The function of the magnetic clutch and brake unit 14 is to detachablycouple the motor 12 to the gearing 16. A unit of the type disclosed inmy U.S. Patent No. 2,618,368 entitled Magnetic Clutch and issuedNovember 18, 1952, may be used to advantage for this purpose. As thepatent reveals, the main advantage of the magnetic clutch and brake unitis to automatically operate when the output shaft has been driven to adesired position and the motor de-energized, to hold the shaft againstmovement under the influence of externally applied loads. The unit 14has further utility in selected applications, Where it may beautomatically actuated to detach the motor from its reduction gearingand thereby permit two actuators, when driven as a pair, to be driven byone drive motor, should one motor fail.

The limiting mechanism 18 is enclosed in a separate housing 22 which, inturn, is detachably secured to the housing of the motor 12 and magneticclutch and brake unit 14. Rotatably mounted within the housing 22 is acam shaft 24 having an end portion 26 projecting through a bore 27 in anend plate 28 of the housing 22. This end portion 26 is receivable in amating bore 30 in the output shaft 20 to detachably connect the twoshafts in axial alignment with one another. Preferably, in order toinsure that the shafts 20 and 24 rotate in unison, they are keyedtogether by making the end portion 26 and mating bore 30 non-circular inshape. Since the housing 22 and the cam shaft 24 are both detachablyconnected to other actuator parts, the limiting mechanism 18 may bereadily separated from other major components without disconnection ofany electrical circuits.

Rotational mounting of the cam shaft 24 within the housing 22 isaccomplished by journaling the shaft 24 in the bore 27 in the end plate28 at one end and in a bore 31 in an upright support 32 fixed to thehousing at its other end. Bearing support is enhanced by securingbearing sleeves 34 to the opposite ends of the shaft, which sleeves, inturn, contact the opposed bearing surfaces on the plate 28 and support32. The sleeves 34 are each keyed to the shaft 24 by any suitable meansas, for example, by the half-moon key 36 (FIGURE 3), so as to as torotate with the shaft.

A pair of cam assemblies 40 and 42 are mounted on the shaft 24 andarranged to move axially relative thereto, responsive to rotation of theshaft. The functions of these assemblies are to actuate switches 44 and46 (FIG- URE 2), respectively, in predetermined limit positions of theoutput shaft to de-energize the drive motor 12. This serves to limitrotation of the output shaft 20 in clockwise and counterclockwisedirections.

In order that the assemblies and 42 move in translation responsive toshaft rotation, each includes a flanged nut or collar 48 and acooperating disk-shaped brake 50. The nut 48 embodies an axial sleeve52, which is internally threaded for engagement with threads provided onthe shaft 24, and a radial flange 54. Each brake 50 is receivable on thesleeve 52 of its nut 48 and engages in face to face relationship withthe flange 54.

Rotation of the brakes 50 with the shaft 24 is prevented by providingeach of them with a radially extending arm 56 that engages a guide rod58 supported between the end plate 28 and support 32 on the housing. Therod 58 is arranged parallel to, but slightly offset from, the cam shaft24. In the illustrative case, the arms 56 are forked at their lowerends, as best shown in FIGURE 3, for the reception of the rod 58. Thebrakes 50 are thus free to move axially relative to the shaft 24 and rod58, but are held against rotation.

It is normally desirable to restrain the nuts 48 against rotation withthe shaft 24 in order that the assemblies 40 and 42 will be caused tomove axially in response to rotation of the shaft. To this end, annularspring washers 62 are provided to yieldably urge the brakes 50 intofrictional engagement with their flanges 54. Each spring 62 bearsagainst one of the brakes 59 and against annular backup washer 64 which,in turn, is held in place by a snap ring 66 receivable in a peripheralgroove in the nut-sleeve 52. It will be appreciated that the spring 62is sufiiciently strong to overcome friction between the engaging threadsof the nuts 48 and shaft 24 to yieldably restrain the nuts againstrotation with the shaft. Adjustment of the relative positions of the camassemblies on the shaft 24 may be accomplished by simply rotating agiven nut 48 relative to the shaft 24. During such adjustment, slippagetakes place between the frictionally engaging surfaces of the nut 48 andbrake 50.

As noted above, switches 44 and 46 on the housing 22 are adapted to beactuated by the cam assemblies 40 and 42, respectively, at the limitpositions of the output shaft 20. The switches are positioned adjacentopposite ends of the cam shaft 24, the switch 44 being located adjacentthe right hand end of the shaft, as viewed in the drawing, and connectedin the energizing circuit of the motor 12, which causes clockwiserotation of the output shaft 20. Likewise, the switch 46 is positionedadjacent the opposite end of the cam shaft 24 and connected in thecircuit of the motor 12, which brings about counterclockwise rotation ofthe shaft 20. Upon actuation of a given switch, its respective motorcircuit is de-energized, so that no further rotation takes place in thatdirection. Actuation of the switches takes place by virtue of fingers 68on the lower ends of the brake arms 56 engaging switch arms 79 in themanner shown in FIGURE 2.

In normal operation, assuming the cam assemblies 40 and 42 to have beenadjusted so that they actuate their respective switches 44 and 46 at thedesired rotational limits of the output shaft 20, the motor 12 isenergized to rotate the output shaft in the desired direction. With themotor energized for clockwise rotation of the shaft 28, the camassemblies 40 and 42 move axially on the shaft 24 from left to right inthe drawing or toward the clockwise switch 44. As previously explained,the brakes 50 serve to restrain rotation of the nuts 48 with the shaft24, and thus the assemblies 40 and 42 maintain their original spacing.Such operation continues until the clockwise switch 44 is actuated tode-energize the drive motor 12 and terminate rotation of the outputshaft 20.

As long as the switch 44 is actuated, further operation of the actuatorin a clockwise direction cannot take place. However, the motor 12 may,of course, be energized to rotate the output shaft 20 (and cam shaft 24)in a counterclockwise direction. This results in the cam assemblies 40and 42 moving toward the counterclockwise switch 46 at the opposite endof the cam shaft 24. As soon as the cam assembly 40 has been carried outof engagement with the switch 44, that switch closes, and the motor 12may again be energized to rotate the output shaft 20 clockwise. Uponcontinued counterclockwise rotation of the output shaft 20, the camassembly 42 will actuate the counterclockwise switch 46 to deenergizethe motor 12 and terminate rotation of the output shaft 20 in thatdirection.

An important feature of the actuator of the invention is that thefrictional coupling between the nut 48 and brake 50 of each cam assemblyserves to protect the limiting mechanism from damage in the event of amalfunction. In this connection, if either switch fails, the camassemblies will be carried into mechanical stops comprising the innerends of the bearing sleeves 34 On the cam shaft 24. The engaged assemblythen maintains its axial position with slippage taking place between thenut 48 and brake 50. For example, if the clockwise switch should fail,as the shaft 24 is undergoing clockwise rotation, the assembly 40 willmove to the position shown in FIGURE 3, where its nut 48 engages the endof the bearing sleeve 34. That nut then rotates with the shaft 24,overcoming frictional restraining force applied by the brake.

Should clockwise rotation of the cam shaft 24 continue, the second camassembly 42 will move axially toward the assembly 40, and eventually itsnut 48 will abut the rotating nut of the assembly 40 and commencerotating with it. Relative rotation then takes place between both pairsof nuts 48 and brakes 50 and will continue to do so until the actuatoris either stopped or reversed. As will be appreciated, the camassemblies can be adusted after such a malfunction takes place, becausethe parts have been prevented from being damaged.

Positive engagement between the cam assemblies and their mechanicalstops on the shaft 24 is insured by providing matching sets of jaws 72and 74 on the bearing sleeves 34 and nuts 48. The jaws 72 on the sleeves34 rotate with the cam shaft 24 and, therefore, when the jaws 74 on thenuts 48 engage the former, the nuts 48 are forced to rotate with the camshaft 24 and are prevented from jamming.

To enable the nuts 48 to rotate with respect to their associated brakes50 without damage to the mechanism 18, while at the same time affordingample friction between them to normally restrain relative rotation, thenuts are preferably made of bronze and the brakes of steel. Since theparts are disposed in face to face relationship, a bronze on steelbearing relationship exists, and the continued rotation of the nuts 48does not result in damage to the assemblies or in excessive loads on themotor.

As explained above, manual adjustment positions of the output shaft 20is effected simply by moving the cam assemblies 40 and 42 axiallyrelative to one another on the cam shaft 24.

In order that the output shaft 20 may have the desired range ofrotational movement, it is necessary that the spacing of the switches 44and 46 be sufficiently great that, when the assemblies 40 and 42 arepositioned immediately adjacent one another, the shaft is still able tomove between its limit positions. The range of movement of the outputshaft can, of course, be increased by changing the thread design of thecam shaft 24 and nuts 48 by increasing the switch spacing, as well asthe length of the cam shaft 24.

Another advantage of the self-protecting clutch feature of the limitingmechanism 18 is that it may be used to set the cam assemblies 40 and 42in positions corresponding substantially to the mechanical limits of thedriven device. This is achieved by temporarily shorting the switches 44and 46 and, with the assemblies initially spaced apart a distancegreater than their final spacing, driving the device first into onemechanical limit and then into the other.

Assuming the output shaft 20 is first rotated in a clockwise direction,the cam assembly 40 will be carried into its stop and will remain therewith relative rotation taking place between its nut 48 and brake 50until the driven device reaches its mechanical limit. At that time, theactuator is reversed so that both cam assemblies 40 and 42 will beginaxial travel in the opposite direction on the shaft 24 until the camassembly 42 engages its stop. Then, as explained above, its axialtravel, of course, ceases, but the other assembly 40 moves toward it anduntil the driven device reaches its mechanical limit in thecounterclockwise direction. The actuator is then de-energized, and thelimits of the cam assemblies are substantially in coincidence with themechanical limits of the driven device.

Final precise adjustment is normally accomplished manually by rotatingthe nuts 48 in small increments. The switches 44 and 46 are finally putback in operation, and whenever the driven device just approaches one orthe other of its mechanical limits, one of the earn assemblies willactuate its associated switch to de-energize the motor. Moreover, asexplained in detail above, if switch actuation should fail tode-energize the motor, then the assemblies will move into theirrespective stops and maintain that position without resulting damage tothe limiting mechanism.

It will be understood that in the illustrative embodiment of theinvention, the output shaft 20 and the cam shaft 24 continue rotating inthe evenut of a malfunction, even though slippage is taking place in thelimiting mechanism. This apparent problem may be solved by providing atorque limiting clutch on the driven device or between the output shaft20 and the driven device. However, should it be desired to incorporate atorque limiting clutch in the actuator itself, this, of course, may bedone. In this connection, the torque limiting clutch, such as disclosedin my US. Patent No. 2,668,426 entitled Torque Limiting Clutch andissued February 9, 1954, may be used quite effectively for this purpose.

Although one embodiment of the invention has been illustrated anddescribed with a certain degree of particularity, it will be understoodthat this was only by way of illustration and that various changes inthe details of the construction and arrangement of the various parts maybe made without departing from the spirit and scope of the invention.

I claim:

1. In an electromechanical actuator having an output shaft rotatable inopposite directions to move a device between extended and retractedpositions and a reversible motor coupled to said shaft, a limitingmechanism comprising:

a frame;

an externally threaded cam shaft rotatably mounted on said frame andcoupled to said output shaft;

a pair of switch means on said frame actuatable for deenergizing saidmotor;

a pair of nuts threadedly engaged on said cam shaft for axial movementrelative thereto, each of said nuts including a radial flange;

a pair of brakes mounted in face to face relationship with respectiveones of said nut flanges, said brakes being held against rotationalmovement, but being free for axial movement relative to said cam shaftwith respective ones of said nuts;

spring means carried by the nut of each brake-nut pair for yieldablyurging the brake of that pair against its nut-flange to restrain the nutagainst rotation with said cam shaft;

means on said brakes and engageable with respective ones of said switchmeans to actuate said switch means substantially when said output shafthas turned through a predetermined number of revolutions necessary toplace said device in its extended and retracted positions;

and stop means mounted at opposite ends of said cam shaft and rotatabletherewith, said stop means engaging adjacent ones of said nuts when saidoutput shaft has turned through a number of revolutions greater thansaid predetermined number.

2. In an electromechanical actuator having an output shaft rotatable inopposite directions to move a device between extended and retractedpositions and a reversible motor coupled to said shaft, a limitingmechanism comprising:

a frame;

a cam shaft rotatably mounted on said frame and coupled to said outputshaft;

a pair of switch means mounted on said frame and actuatable forde-energizing said motor;

a pair of cam assemblies adjustably and movably mounted on said camshaft and each having shaftengaging means rotatable with said cam shaft,whereby its assembly maintains a given axial position on said cam shaft,and rotatable relative thereto to cause its assembly to move axiallyrelative to said cam shaft, said assemblies engaging respective ones ofsaid switch assemblies for actuating the same; and

frictional clutch means on each of said assemblies normally restrainingsaid shaft-engaging means against rotation with said cam shaft to causeits respective cam assembly to move axially as aforesaid and responsiveto blocking of such axial movement of its respective cam assembly topermit said shaft-engaging means to rotate with said cam shaft.

3. In an electromechanical actuator having an output shaft rotatable inopposite directions to move a device between extended and retractedpositions and a reversible motor coupled to said shaft, a limitingmechanism comprising:

a frame;

an externally threaded cam shaft rotatably mounted on said frame andcoupled to said output shaft;

switch means mounted on said frame actuatable for de-energizing saidmotor;

a cam assembly including a nut mounted on said cam shaft in engagementwith said threads, whereby relative rotation between said nut and shaftcauses said nut to move axially of said shaft, a brake mounted inface-to-face relationship with said nut, and means on said nut urgingsaid brake into frictional engagement with said nut to restrain relativerotation thereof;

means on said frame in engagement with said brake to prevent rotationthereof, but to permit axial movement thereof relative to said camshaft;

and means carried by said assembly and engaging said switch means foractuating the same.

4. The subject matter of claim 2 including stop means mounted atopposite ends of said cam shaft for rotation therewith, said stop meansbeing engageable with respective ones of said cam assemblies to blocksuch axial movement.

5. In an electromechanical actuator having an output shaft rotatable inopposite directions to move a device between extended and retractedpositions and a reversible motor coupled to said shaft, a limitingmechanism Comprising:

an externally threaded and rotatable cam shaft coupled to said outputshaft;

switch means actuatable for de-energizing said motor;

a nut mounted on said cam shaft in engagement with said threads, wherebyrelative rotation between said nut and shaft causes said nut to moveaxially of said shaft;

a brake mounted in face-to-face relationship with said nut;

means on said nut urging said brake into frictional engagement with saidnut to restrain relative rotation thereof; guide means parallel to andoffset from said cam shaft, said guide means being engaged with saidbrake t0 prevent rotation, but to permit axial movement thereof relativeto said cam shaft; and

means on said brake engaging said switch means for actuating the same.

References Cited by the Examiner 5 BERNARD A. GILHEANY, PrimaryExaminer.

ROBERT K. SCHAEFER, D. J. WILLIAMOWSKY,

Examiners.

5. IN AN ELECTROMECHANICAL ACTUATOR HAVING AN OUTPUT SHAFT ROTATABLE INOPPOSITE DIRECTIONS TO MOVE A DEVICE BETWEEN EXTENDED AND RETRACTEDPOSITIONS AND A REVERSIBLE MOTOR COUPLED TO SAID SHAFT, A LIMITINGMECHANISM COMPRISING: AN EXTERNALLY THREADED AND ROTATABLY CAM SHAFTCOUPLED TO SAID OUTPUT SHAFT; SWITCH MEANS ACTUATABLE FOR DE-ENERGIZINGSAID MOTOR; A NUT MOUNTED ON SAID CAM SHAFT IN ENGAGEMENT WITH SAIDTHREADS, WHEREBY RELATIVE ROTATION BETWEEN SAID NUT AND SHAFT CAUSESSAID NUT TO MOVE AXIALLY OF SAID SHAFT; A BRAKE MOUNTED IN FACE-TO-FACERELATIONSHIP WITH SAID NUT; MEANS ON SAID NUT URGING SAID BRKE INTIFRICTIONAL ENGAGEMENT WITH SAID NUT TO RESTRAIN RELATIVE ROTATIONTHEREOF; GUIDE MEANS PARALLEL TO AND OFFSET FROM SAID CAM SHAFT, SAIDGUIDE MEANS BEING ENGAGED WITH SAID BRAKE TO PREVENT ROTATION, BUT TOPERMIT AXIAL MOVEMENT THEREOF RELATIVE TO SAID CAM SHAFT; AND MEANS ONAID BRAKE ENGAGING SAID SWITCH MEANS FOR ACTUATING THE SAME.